I used Google to search for wmctrl -a and window id.
The first hit was a link to a revision at Ask Ubuntu:
And clicking it gave me this link in the address bar:
https://askubuntu.com/revisions/865e9305-bef6-4397-9097-2848d0dc1233/view-source with the following contents:
But I can't figure out where that revision originated. How do I find the corresponding question or answer?